I need to know what is running on your mac so I can tell you what may or may not need to be done, If you are running a lot of applications or if you had a lot of traffic for the web server, Then of course I would suggest that you move it off your machine.
Depending on what program you are using for the webserver the database engine may be getting corrupted, so it would need to be cleaned, Or your webserver may be nder attack from an outside user that wants to hijack your email server for their spam usage.
If you are running applications that store a lot of data, then it may be your drives are getting full, In which case you will need to clean them up as MAC's use the available disk space as what is known as a swap file, so that the less space you have available the smaller the swap file and this will degrade performance.
There are a lot of considerations when it comes to what may be slowing your machine down, however without knowing what apps and how many you are running, There is nothing I can suggest.
So I will opt out and see if another Mac expert can help you with this.