i'll share some setup that i used and planning to use in the future
currently using
Guitar -> Amp (Line 6 15 W) -> Mixer -> M-audiosoundcard -> Studio monitor
with this setup, there is no need for a mic and the signal i get would be very clean. the monitor i use is the same in the mixdown. latency and accuracy is not a problem 'coz the soundcard does the job for these factors. the mixer serves as my pre-amp where i adjust the level, trim, and low mid high eq's. however, a mic less setup like this usually doesn't get the 'air' tone in the guitar track .
planned upgrade
Guitar -> Amp (Line 6 75 W) -> Microtube Pre-amp w/digital out ->
Soundcard ...
the bigger amp is capable of producing a wider range of tones because of the built in amp simulation. it's like having a multifx built-in to your amp. The preamp would help me in getting a warmer, louder, sweeter sound from the amp with or without using a mic. Using the digital out makes the signal clean.
... the preamp IMO, is very important because of its function in the signal chain.