The tongue and groove ends should self-space; the square ends should be placed 1/8" apart.

If you are asking about gaps the length of the boards, than they may be required depending on the moisture content of the wood.

A lot of it is damp enough it will shrink in use, but making a mistake of butting dry wood can result in buckling in the summer when the humidity is higher.

Sub floors are routinely left with larger gaps than the finished floor, since it does little harm and a mistake is so bad.

The finished floor needs careful attention to acclimating and the season of the year.

In summer you can acclimate and install a little more snug than in winter.

The boards are GOING to shrink during heating season and expand during cooling season.

Al the nails and finishing the world will not stop this.

Wood moves as its moisture content changes.

Attempts to try and hold it will result in splitting or buckling.

There is a good article about wood moisture meters in the January/February 2010 issue of Fine Woodworking magazine, pages 64-68.

If it's a rather old house the gaps may be there from the subfloor having been laid with a fairly high moisture content. In this area it was typical that 1x6 subfloor served double duty- first as the forms for the poured concrete foundation walls, then as the permanent subfloor. Needless to say, it underwent some shrinkage after installation, and the T & G's all but shrank beyond the matching.
Casey