I have heard people say that they can be bad. Are there ways to compensate for missed Shraddhas?
The ancestral offerings are more important than the performance of rites dedicated to gods. Anyone not doing them properly becomes impure and hence unfit to perform any other rituals. And, this impurity is a permanent one unlike the impurities related to birth/death.
Manu Smriti 3.203. For twice-born men the rite in honour of the manes is more important than the rite in honour of the gods; for the offering to the gods which precedes (the Sraddhas), has been declared to be a means of fortifying (the latter)
Daily impurity is for one who is addicted to gambling, etc., and for a dependant. The impurity of a person, who does not perform the S'raddhas, ends with his ashes (i.e., death). (10)
Temporary impurity is not for them, but a lifelong one. Thus impurity according to the differentiation of merits has been spoken of. (11)
Daksha Smriti, Chapter 6
Further consequence will be facing the wrath/curses of the disappointed/angry Pitrus as mentioned in Atri Smriti/Samhita:
Wealth, sons, and the family of the householder, who does not perform the S'raddha when the Moon is in conjunction with the Kanya (the sixth sign of the zodiac, i.e., in the dark-fortnight of the month of A's'vin), become destroyed by the sighs of the Manes. (352)
When the Sun is in the Kanya, the departed Mane; get good sons. The region of the dead remains always empty till the seeing of the Vris'chika (the sign Scorpio, i.e., till the Amavasya of the month of A's'vin). (353)
Thereupon, if, at the advent of the Vris'chika (i.e.) on the Amavasya), the departed Manes become disappointed [for the non-performance of the S'raddha], they, imprecating a highly dreadful curse on the son, brother, daughter's son, or son's son, return to their own habitations. (354)
Those, who are devoted to the rites for the departed Manes, attain to the most excellent condition. (355)