If 100% of the active protein is recovered in the pellet, and the pellet is resuspended in 1/10 the volume from which the protein was precipitated, the concentration of that protein will be 10-fold higher than it was before precipitation. (Ignoring the additional volume of the pellet.)

If the yield is lower than 100%, or if the protein loses activity as a result of the precipitation, then the activity in the resuspended pellet will be less than 10-fold higher than it was before precipitation.

If the ammonium precipitation was used as a purification step, the specific activity of the enzyme (activity per mg of total protein) may be higher than it was before precipitation.

Sometimes, a bound inhibitor or activator may be lost during ammonium sulfate precipitation, which could have an effect on the activity measured in the resuspended pellet.

An ammonium sulfate pellet, when resuspended in a small volume, carries over a substantial amount of ammonium sulfate. This should be removed by dialysis or gel filtration if it causes a problem with the subsequent use of the resuspended pellet.

1) if you add 10 ml of buffer, the volume will be larger, because of all the proteins and ammonium sulphate, so that decreases your protein's concentration

2) usually, some of the activity is lost either because of loses during the procedure (some protein stays in solution, loses during centrifugation, decanting etc) or because the activity is lost (denaturation etc.), so that will decrease your total (and hence also per ml) concentration of your protein

3) if you salt out directly to 80%, there won't be big purification fold, so your specific activity will be more affected by the loss of activity as in point 2

In conclusion, yes, you should concentrate your protein, but it's not as straightforward as to say it will be concentrated 10-times.