I've put out 5 albums, 2 EPs (one of which is more like a 5-track double single -- i.e. 2 songs, with the main recordings of each song plus some remixes), and somewhere north of 50 singles since 2006, and I'm currently finishing up a 6th album. I started out using Tunecore in the early days, but their pricing at the time was not economical for me due to having to pay the same fees per release every single year, so I switched to CD Baby, and have used them for almost all my releases since then. The one exception is that CD Baby stopped doing the licensing for cover songs in the last year or two, so I've started using Soundrop for (non-public domain) cover songs for the last year or so.
One thing I will say is that CD Baby has been an excellent distributor, getting songs to pretty much everywhere, whereas some of the newer distributors don't have quite as wide of coverage (Soundrop is in that category, even though they have the same parent company as CD Baby), but they're also far from the most economical distributor to use if you're regularly putting out a bunch of releases. In particular, we're talking about $15 per single (or $10 if you get a "half price" sale -- they still charge you the full fee for the UPC code), and they still take a 9% commission, but the distribution fee is a one-time fee. (I don't recall their album plus UPC fees off the top of my head, but I'm thinking more than $45 and less than $50? -- I tend to make my purchases when they have sales and use them later.) Some others charge an annual fee (and may or may not take a commission), but you have to keep paying that fee every year, but they give you unlimited releases. I've definitely released enough music in the last half decade that I could get a better deal with those sorts of arrangements *if* I continue with the same sort of output level. I think it's possible Tunecore may have recently switched to that sort of arrangement, but don't quote me on that as I may be remembering wrong.
Beyond picking your distributor, you'll also want to make sure your songs are registered with the MLC (Mechanical Rights Collective) for collecting on-demand streaming (and certain download) mechanicals in the USA and a performance rights organization to collect the performance royalties for the streams wherever the songs get played. That leaves out foreign mechanicals collection, which would need an arrangement with an administrative publisher to collect mechanicals from other countries (or you to have direct arrangements with a bunch of foreign mechanicals societies). (That is where CD Baby Pro and such come in, but, at least for me, my foreign numbers aren't high enough to offset the cost of such arrangements.) Oh, and SoundExchange collects portions of the digital recording royalties that don't go through the distributor. How much money is being left on the table in most of those cases will depend on your numbers, though. I'm still at the few pennies level from the MLC (and not enough to meet their threshold for payment), but I get some cents here and there from ASCAP (for the streaming side of things -- most of my ASCAP money, and what gets me over the threshold for payment, comes from live performances of my own songs), and, of course, royalties from CD Baby -- by no means as much as I've paid them to date.
But as to the underlying question of putting songs on Spotify (and Apple Music and Amazon Music and TenCent and etc., etc., etc.), I write songs so people can hear them. While I play live regularly, getting the recordings out into the world is another part of not letting those songs sit on the shelf, and they do get plays, even if not the millions needed to make decent money from them. Funnily enough, one of my songs, from an album I put out in 2019, has recently gotten upwards of 10K plays on TikTok, mostly in the Middle East and other nearby areas (e.g. North Africa, Turkey, ...). Unfortunately, the largest percentage of those are ones that don't even pay a micropenny, no less more money.
Rick