Are there applications where slotted holes should be avoided?
Slotted holes are used only where some ‘play’ in adjustment is anticipated. They should never be used in situations that require the full grip strength of the connection. For example, in a steel framed building. Oftentimes the beams (horizontal members) are fastened to the columns (vertical members) with bolts, usually with a clip angle. The position and number or the holes is critical to allow the maximum developed strength. In general, a bolt hole is only 1/16 inch larger than the bolt diameter. This is just enough clearance to align the pieces and the bolts, and allow enough metal to metal contact to grip the members between the bolt head/washer and nut/washer.
