All Filters including an Inline Filter are designed solely for preventing un-dissolved Particulate Matter from reaching the Analytical Column or the HPLC Instrument. Note that the analytical Column does have Porous Frits on the inlet (and outlet) that will also prevent some un-dissolved Material from reaching the Column bed, but if they become clogged, they may be difficult to remove and the Column is no longer be usable.
A Guard Column will also perform this function but not as well, in addition to its primary purpose of retaining matrix contaminants that would otherwise end up at the head of the analytical Column. If a Guard Column is not properly matched to the analytical Column, it could degrade your Chromatography. However, if all you need is to filter out Particulate Matter, you should choose an Inline Filter over a Guard Column since the former are less costly.
When the Inline Filter becomes clogged with Particulate Matter, it can simply be replaced with a new one, as they are designed to be disposable. We recommend that all Cogent HPLC columns be used with Inline Filters to increase their lifetimes.
Rule of thumb is that a Guard column is a Chemical Filter and an Inline Filter is a Particle Filter.