I always manual save before a stretch of doing anything new (exploring an area, progressing a quest, etc.). I make gratuitous use of quick-save as well (if I screw something up, the nearest manual save is never too far back).
I save often enough to run out of slots in ME2 (I don't even remember the limit in ME3; I never played the series again after beating it once). Since I play on PC, I always just copied the save folder and then trashed most of the manual saves (also, the interface actually handled more than the limit, so when you were done playing, you could put them all back in the save folder and load any of them up—you just can't get it to make a new save anymore); that way, I had all my progress still around when importing into the next game.
I haven't really played it yet, but if I do, I suspect my behavior will be the same with the remaster.
Around 80 - 90 per playthrough of one game. Why? Because I can and the game allows it. Is ist really necessary? I suppose not, but what is necessary that there are enough recent saves left in case something goes wrong: accidently picked the wrong answer, dying after a longer period of fighting, an unexpected bug or glitch or simply forgeting something before moving on. I had to learn the hard way that the almighty autosave isn't enough to deal with all situations. Saving manually on different slots sure came in handy during the years quite often. And after retiring a character, I simply delete most of the saves.
Save files are small in size and are easy to create. I don't say all people should create a huge amount of saves as I do, but at least consider a rotating system of at least 5 - 10 hard saves: saving before leaving the Normandy, before starting a main mission, saving before difficult choices, or prolonged fights. And I think this should be naturally with all roll playing games.
Over the years, a significant amount of problems in various other RPG supporting boards (Witcher series, Fallout series, Elder Scrolls, Gothic/Risen/Elex series) would've been solved or never even posted in the first place, if the OPs simply had saved on a regular basis. CDPR introduced three rotating auto save slots with Witcher 3, Piranha Bytes even six rotating slots for Elex as a consequence.
ME1 73 saves, ME2 93, ME3 99 (missed lots of places like Palaven's moon)
