There are two kinds of “bleeds” for brakes. There’s a mini-bleed (I’ve also heard it called a bubble bleed) and I tend to do that every couple-few(tm) weeks since I learned to do it. It’s not a full/true bleed; you’re really just getting air out of the system.
A full bleed I tend to do once a year, but I may do it more often than that if I keep riding as often as I do.
Mini-bleeds are fairly easy; full bleeds are more time consuming. Anyone who is unaware of how to do either can find vids from GMBN, Park Tool and even Seth’s Bike Hacks/Berm Peak all on YouTube.
I only bleed my brakes when they need it, which isn’t very often and can sometimes be many years. I have an 11-year-0ld bike with about 20,000+ miles on it and I don’t think the brakes have ever been bled and they still work fine. If it ain’t broke, don’t fix it.
Brake bleeds are done on an as needed basis. Doing it when levers are firm and working properly is generally a practice session.
Fluid types. DOT and mineral oil.
DOT does two things, absorb air and moisture, thus only fresh fluid shall be used. DOT MUST be degassed before use! Do this step each and every time to avoid bubbles forming in a week or three… DOT cleans up with water, a mist sprayer will rinse it away if any spills over onto painted surfaces during a bleed.
Mineral oil, no worries with air and water permeation! No need to degas prior to use. Clean up is simple enough with a mild solution of Dawn and water. Mist sprayers loaded with Dawn and water ease the cleanup and a followup with a water rinse to get rid of soap residue.
A bleed is a simple process to remove a bubble or a few of em.
A flush is the complete change of fluid and bleed.
Carrying a bike on the exterior of your car, beware of rain and interstate speeds. Rain can be driven into the master cylinders right past the seals at high speeds. Bag the bars or transport the bike inside to avoid water contamination. DOT can have serious failures and mineral oil can too. Since this can go unnoticed, the system can be severely damaged overtime from corrosion.