You can add a live bass and drum loops to both standalone and pc...it's a bit more complex with a standalone, but it can be done.
Depending on how the standalone records (hard drive, flash memory, etc.) you can import your recordings to the computer for editing and mixing. Many units have a USB port that allows you to directly connect it. Others use memory cards like SmartMedia and you can get an external card-reader for your pc to import them.
What will you miss out on with a standalone?...probably the excellent graphical interface that a pc offers...how the software is laid out, etc...and don't forget the large monitor, not a little LCD square

. I also like the feeling of working with a computer better than with a standalone.
Some of the higher-end units do have MIDI sequencing, but computers really outperform them as far as MIDI goes.
My advice...if you have a PC with decent specs, go with the computer-based system. It's much more straight-forward and will save you tons of headaches (I first started with a standalone and then switched to a PC...haven't looked back since

)...computers are much more powerful and with the vast amount of software avaliable, it will grow with you.
I am not against standalone recorders...I'm just a pc user, so...

. Actually, I'm very impressed with the new powerful standalones that are coming out, particularly the Roland V-studios. Some of them certainly do rival computer-based set ups.