The majority of the benefits that come with OSRS Gold having a high Smithing level come from the Quest and Achievement Diary requirements for completing certain tasks.
Quest Requirements
There are numerous quests available in OSRS with a Smithing level requirement to be completed. One of them is Dragon Slayer II, which requires Level 70 Smithing to finish.
Complete list of Quests that require Smithing levels are as in the following order:
Niveau 4 - Zogre Flesh Eaters
Level 20 - Elemental Workshop I
Stage 20: The Tourist Trap
Level 30 - Elemental Workshop II
Level 30 - One Small Favour
Niveau 40-Family Crest
Level 45 - Swan Song
Level 50 - Between the Rocks...
"Level 50" Cabin Fever
Level 50 - Legends' Quest
Level 65 - Devious Minds
7th Level - Dragon Slayer II
Diary Requirements
Also, a lot of Achievement Diaries in OSRS have Smithing requirements for levels to complete. Diary rewards can be more valuable than Quest rewards that are available in the game, therefore this may act as a strong incentive for players who want to move up their Smithing skill.
Smithing Quests XP Rewards
There are also a variety of quests that give Smithing the XP. It's a good idea to finish them prior to reaching Level 99 when you feel the XP rewards are worth it.
Now is the time for you to transliterate those research notes. It's up on you to translate them. The complete set can be seen in the image. The colors of the buttons can be changed by simply pressing on them.
The notes translated
Talk to Ava after you have completed notes. Ava will request that you present some polished buttons and some hard leather to finish the device. Polished buttons can be found from pickpocketing H.A.M. Members or simply from at the Grand Exchange. Then, you'll get 50 crafting XP as well as A pattern. Combine those with the polished buttons and a bit made of leather to form containers.
The quest will be complete after you've given the Buy RS Gold container back to Ava. Congratulations!