Two questions really. First, can space maranies recover their Drop Pods or are they one use things. I know there are landers large enough to drop landraiders I guess they may be large enough to recover Drop Pods. If Drop Pods are disposible, then does that mean that space marines always need some other transport, like a Thunderhawk, to get them back into space. Since Space Marines are so few in numbers I can imagine recovering troops and material so that they can be quickly re-deployed would be paramount.
Second Question: How does the Empire land and recover Titans. Those things are huge. Does the Imperial Guard / Imperial Navy just have supper huge dropships. Does the Adeptus Mechanicus have their own dropships for Titans. Titans like space marines are such a valuable military resource, I can not imagine that a commander could afford to leave them on a planet any longer than nessisary before redeploying them to the next battlefield.
Drop pods are not used as an every-battle conveance. Contrary to every SM battle in the tabletop game, drop pods are almost only ever used in the opening engagements of large planetary assaults. Before their use the space marine commanders weigh all the available entry vectors, drop pods are used if a space marine force needs to get an entire company on the ground fast and/or the marine's ship can't stay in orbit for long. Marines will not, I repeat, will not drop in with drop pods, fight 1 battle, then jet back up to the strike cruiser just so they can drop pod into another battle. Drop pods are a start of war thing. They are not perfectly safe, shooting 1 at a planet all by its lonesome is a sure way to get it blown out of the sky, especially if its target is anywhere near enemy concentrations. They are more or less one-use items. Since space marines generally plan on sticking around awhile on a planet they drop pod onto their techmarines will go around and salvage any pods they can, but all the pods shot are write offs the moment they leave the chute, if they get salvaged, all the better.
Titan landers are so massive they cause enough atmospheric disturbances on a planet to cause thunderstorms to form for several days around the landing sites (on planets which can have thunderstorms). They carry the titans, mechanics, support staff, replacement parts, ammo, fuel, and skittari the legion needs to fight with. These things and their titans are sent to really really big fights. Commiting a titan strike force, or even worse a whole legion is a massive undertaking. They are not lightning strike-teams, going in and out in 5 minutes flat. It takes months or years of planning before a titan force is landed on a planet (not withstanding transport times). Once there, the titans are there practically until whatever fight is there is over. If the fight turns ****-up, getting titans off planet quickly under emergency conditions is very risky, dangerous, and expensive. With a majority of their support stuff (billions in Imperial thrones worth, but infinately easier to replace than a titan) and probably a good portion of its skittari (fighting a holding action) left behind.