Some asteroids or comets dont have enough minerals to warrant building and shipping new mines there (plus the time) but moving a huge miner there and letting it mine is easy. Just need to ship a mass driver whenever I feel like it to send it all home.
I usually go > Big Sorium Harvester (about 70 harvesters, 30m fuel storage, hub) > automines + mass driver on most needed stuff and then depending on situation either colonisation + terraform + normal mines or 2-3 Big orbital miners (each with 80-100 modules, at about 500k tons). Good thing about miners and harvester stations when build big enough is, with improving tech they will get better, just needs enough of modules (and fuel storage for sorium) even for super late game stuff.
Edit:
My general reasoning is, below 10k minerals I leave it to CMC and buy or tax as needed. Above 10k, depending on amount of minerals I send automines or orbital miners (the less minerals it has the bigger chance I will send orbital), automines have quite a bit of hidden cost in having to use and fuel transports that are also busy for some time, while huge orbital miner only needs a tug, and even that only once in a while. With about 100k minerals (total) or more I almost exclusively use automines, if the colony cost is too high or its outside of gravity limits.
Also, which is probably well known, a target with 5 minerals at 10k each is better than one with a single mineral at 50k, because one mine can mine its annual production of every mineral.