When bearings are housed in metal block also called pillow block, they are protected from accumulating grease and dust. Bearings are the most important in any motor and also expensive to replace. Pillow blocks are held firm on a metal mount safely bolted.
Oh yes, I hear you; enough of engineering education. In fact, I too thought so when the shopkeeper was explaining to me the other day. I rudely interrupted him and told my needs and asked for a matching recommendation.
I think he guessed my poor knowledge of bearings, bolts and nuts. He hid his displeasure somehow and showed me several pillow bocks to choose from.
Ah, again my expression revealed my lack of knowledge. I gave in and sought his help in buying what I exactly needed.
If you ever need a pillow block, it is advisable to gain some knowledge about it before buying.