The bridge must always remain perpendicular to the top of the instrument. Tuning at either end tends to warp the bridge and, if not adjusted frequently, this warping can become permanent. Ask your teacher or repairman for assistance. If not frequently straightened, the warp can become so severe that the bridge can break and the force in the collapse can seriously damage the top of the instrument.
The top of the instrument absorbs moisture during the summer and can puff up causing the bridge to also push up and become too high. Likewise, during the winter, the top of the instrument can flatten causing the strings to become too close to the fingerboard. It may be necessary to have two bridges, one low bridge for the summer and one higher bridge for the winter. The E string on the violin and A string on the cello should have some protection to keep them from cutting down into the bridge.
The bridge height is also dependent on the shape of the fingerboard. Any warping and/or inconsistencies in the fingerboard can force a luthier to adjust the bridge rather than reshape the fingerboard. This may make some notes a little harder to play but in the end the instrument will produce a better sound than other means of repair .