[Goosegirl]

Do you follow the guidelines as to how far apart you plant your veg in a raised bed? If the packet says 6" apart and 12" between rows, do you take the middle line as advised and plant them out in a staggered pattern so all plants are 9" apart?

[mumofstig]

If you have good fertile soil, then you can plant at closer spacings.
If you have your average soil then I personally don't think that closer spacing works, unless you are after miniveg 
I tried it a few times with very mixed results, so went back to normal spacing

[Plot74]

Some plants will tolerate been close together others won't.
Give them room to grow and let the air circulate round them
Most salad stuff don't mind being cramped  but you harvest them more quickly young plants sometimes taste better.
John

[Trillium]

Depends on the plant. I won't space my toms too close because they really need the space so I stick to 12" in every direction and do alternate spacings on rows (sort of zigzag). Smaller items can be spaced a bit closer but you must be sure the soil has been well fed to accommodate this closer spacing.  Multi-seed pods like beets are done in rows about 6" apart, mostly so I can find them easily, same with chard.  Carrots can be rows or just thrown out if you can recognize the young foliage.