In general charging liquids and solutions is easier and preferred over charging solids. One concerns with charging solids is that not all of the solids may be transferred to the reactor. Charging of liquids is usually completed by chasing residual liquids with a small charge of solvent; for instance, a solution maybe prepared using 95% of the volume specified in the laboratory process description, with 5% of the latter solvent volume being used to complete the transfer.
More specialized equipment is used for charging solids on scale; such equipment may be known as alpha-beta valves, butterfly valves, shot valves, star valves or other names.... Glove boxes have also been erected on top of reactors for charging moisture-sensitive or oxygen-sensitive materials.
Specialized equipment is used to charged gases on scale, with special considerations to minimize any risk of releasing gases. To protect personnel and equipment from leaks of hazardous material such as H2 or F2, the lines used to charge such gases may be encased inside sealed lines or pipe. Charging 37% aqueous HCl is more convenient than charging HCl from cylinders.I've had some experience transferring solids into a solvent-filled reactor recently; although the material was as close to ideal as you could possibly imagine (non-toxic, a nice round shape), it was an incredibly painful process. (I fear that I may be waylaid by an operator for suggesting this particular order of addition, but it (I think) will save us a good bit of time.
In general, I think it is to be avoided -- the specialized equipment above is expensive and does not necessarily guarantee that all the solid starting material will actually make it into the reactor.