There is a difference between grain filling and grain lifting. Grain filling is most often done in timber such as oak that has quite an open grain which bleeds through IMO regardless of how many coats of finish one would put on eg. shellac/varnish/hard wax oil. Some people like that open grain effect but if it's a perfectly smooth surface that you want then you do need to grain fill.
Here's a photo of an open grain
and after a bit of grain filling
Grain lifting occurs when small fibres swell as a result of water/moisture. Once dry, these can be denibbed with a light sanding. However, this has no effect on any open grain.
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