Unless there are real problems doing so you should not just rely on a mask for high risk tasks. There are some very good reasons for this including:
High risk tasks can produce so much dust that the mask cannot give the amount of protection needed. Also the filter in a mask can quickly become clogged and stop working. A mask only protects the person wearing it. Anyone else in the area could still be at risk from the dust if they do not wear a mask as well. There are many common mistakes that people make with masks. These include choosing the wrong type, not being face fit tested or not wearing them properly. As already mentioned the main aim is to stop the dust getting into the air in the first place. If you do just rely on a mask for high risk tasks you may be asked to justify why.