The tick events are handled through messages sent via the message pump. In
the case of windows forms timer events, the messages can build up and
saturate the pipeline causing the code to run badly. Once the message
pipeline is full, new messages cannot be added so possibly many messages,
not just timer events, will be missed. Up to a certain limit, all messages
will be recorded and the performance will just degrade noticably.

Using the System.Timers.Timer you can have timer messages handled on another
thread. This is more accurate but should still not use a handler that takes
longer than the timer interval, at least, not without some sort of
synchronization mechanism.

Generally, you should ensure that timer handlers of all types are quick and
efficient and use as few resources as possible.